MySQL 8.0

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select version();


version()


8.0.30


CREATE TABLE mytable(
   id      INTEGER  NOT NULL 
  ,userid  INTEGER  NOT NULL
  ,choices VARCHAR(13) NOT NULL
);
INSERT INTO mytable(id,userid,choices) VALUES (1,3,'1,2,3');
INSERT INTO mytable(id,userid,choices) VALUES (2,55,'5');
INSERT INTO mytable(id,userid,choices) VALUES (3,783,'2,6,7');
INSERT INTO mytable(id,userid,choices) VALUES (4,45,'1,4');
INSERT INTO mytable(id,userid,choices) VALUES (5,5,'1,2,3,4,5,6,7');
select t.userid, j.choice
from mytable t
cross join json_table(
    concat('[', t.choices, ']'),
    '$[*]' columns (choice int path '$')
) j
where j.choice in (1, 2, 3, 4, 7)
order by t.userid, j.choice


userid
choice


3
1

3
2

3
3

5
1

5
2

5
3

5
4

5
7

45
1

45
4

783
2

783
7